Beat surrender: using heart rate to monitor fitness and training

Author

Senior Lecturer in the School of Psychology and Exercise Science, Murdoch University

Disclosure statement

Jeremiah Peiffer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

Within this spectrum, the heart rate (HR) monitor is a relatively uncomplicated method of monitoring exercise intensity by providing real-time measurements of cardiovascular responses to exercise.

The science behind HR monitoring

At the start of exercise, or when changing exercise intensity, a flood of information is sent from the periphery (e.g. muscle and lungs) to the brain indicating a need to modulate blood flow and oxygen supply to the muscle.

In response, HR is increased or decreased as necessary to match blood flow demands. During incremental exercise, HR will continue to increase until reaching maximum (HRmax) after which further increases in intensity have no influence.

HRmax is highly correlated with peak aerobic capacity (the highest level of oxygen-use during maximal exercise) and although the relationship between HR and aerobic metabolism is non-linear, HR is still a good indicator of aerobic intensity.

In addition to real-time monitoring of exercise intensity, HR provides an indication of overall fitness and changes in fitness over time. Normal resting HR is 60-100 beats a minute; but with training, the heart, as with any other muscle, becomes larger and stronger resulting in a greater release of blood per contraction.

As fitness levels increase over time, changes in movement economy (the energy needed for a given workload), increases in overall aerobic capacity and the strength of the heart can lower HR at a given workload. Indeed, measurements of pre- and post-training HR responses to a set workload have been used to monitor fitness changes throughout the literature.

What information do you need to train with HR?

One of the more confusing areas of HR training is the determination of training zones.

For simplicity, these can be referred to in terms of intensity as easy, moderate and hard. Exercise in the easy zone (below lactate threshold or ventilator threshold one) can be sustained for prolonged periods of time (60+ minutes) and makes up the majority of most training programs.

Indeed, recent research examining numerous endurance-based training programs showed up to 75% of all training is within this zone.

Exercise duration is reduced in the moderate and hard zones; but exercise in these zones is necessary for improvements in physiological variables consistent with fitness and health, as well as for athletic performance.

Most HR zones are prescribed as a percentage of HRmax (see table below). Using a maximal exercise test (which involves exercising under increasing workloads until exhaustion), HRmax and training zones can be precisely determined.

This can be expensive; thus, several methods to calculate HRmax are available. Of these, Stevens Creek’s (HRmax = 205 - [age/2]) and Fox and Haskell’s (HRmax = 220-age) equations correlate well with actual values; although caution must be taken as these are predicted values only.

Limitations to training with HR

Heart rate is a global stress variable influenced by state-of-mind and environmental conditions. Significant elevations in HR occur during exposure to heat as the body increases HR to provide blood to the skin for cooling.

During prolonged efforts, especially in the “hard” training zone, HR can drift upward causing individuals to reduce their effort and thus under-train.

Conversely, fatigue can present as an inability to increase HR during exercise and can limit its use.

Finally, HR is influenced by some medications (such as beta-blockers) and individuals should be aware under such circumstances increasing HR beyond a certain point may not be possible. Indeed, attempting to do so may be dangerous.

All you need to do to increase your fitness is just listen – albeit intently – to your heart.